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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 28 |
| 4 | 286 |
| 5 | 3886 |
| 6 | 66260 |
| 7 | 1361972 |
| 8 | 32784353 |
| 9 | 904412593 |
| 10 | 28124223808 |
| 11 | 973106096392 |
| 12 | 37073604836768 |
| 13 | 1541948625066176 |
| 14 | 69513081435903392 |
| 15 | 3376138396206853792 |
| 16 | 175739519606046355540 |
| 17 | 9760024269508314079444 |
[1,1,4,28,286,3886,66260,1361972,32784353, 904412593,28124223808,973106096392,37073604836768, 1541948625066176,69513081435903392, 3376138396206853792,175739519606046355540, 9760024269508314079444] |